The present invention is directed to an improved load-handling clamp capable of handling two or more stacked loads of limited differing sizes, such as vertically-stacked abbreviated-length paper rolls of limited differing diameters. The clamp is also useful for handling stacked paper rolls of approximately the same diameter which, due to winding variations, cannot be handled by a solid arm clamp.
Such load-handling clamps normally consist of at least a pair of separately-actuated clamp arms on one side of the clamp, in opposed relation to a single, larger clamp arm on the opposite side of the clamp. The separately-actuated clamp arms are powered by separate hydraulic actuators connected in parallel to a source of pressurized fluid, and give the clamp the ability to apply clamping force separately to multiple cylindrical objects of different diameters stacked one atop the other. Similar clamping capabilities can also be useful with respect to other types of loads, such as stacked bales or cartons of different sizes.
A common problem with such a clamp is misalignment of the separately-actuated clamp arms due to different frictional resistances in the respective arm mechanisms as they close or open. If the clamp arms are misaligned to any extent, their combined profile will usually be thicker than normal. If the operator is unaware of such a misalignment the clamp arms can strike a paper roll located inside the arms, or adjacent rolls located outside the arms, as the arms are inserted or withdrawn in the course of engaging or depositing a paper roll, causing substantial damage to the roll or rolls. Correction of such misalignment often necessitates opening or closing the clamp arms to their maximum extent to realign them, which is time consuming and requires operating space which may not be available.
A related problem is that, if only a single abbreviated-length roll or other single load is to be handled, clamping pressure on the load-engaging clamp arm cannot be attained until the other separately-actuated arm or arms are closed to their maximum extent. Conversely, opening of the clamp arms sometimes requires full opening of one clamp arm before another can be released sufficiently to disengage a load. In either case, the resultant high degree of misalignment of the clamp arms maximizes the time and space requirements for operating the clamp.
U.S. Pat. No. 4,682,931 offers a partial solution to these prior problems by providing a flow regulator of the divider/combiner type which requires the respective movements (or lack thereof) of a pair of clamp arms during closing and opening to be simultaneous until the regulator is overridden, after which nonsimultaneous movement of the clamp arms is enabled. U.S. Pat. No. 5,984,617 improves on this system by making it compatible with manually-selectable predetermined clamping force adjustment systems. However, such flow-regulating solutions for controlling the movements of the pair of clamp arms cannot adequately keep the clamp arms aligned under all circumstances, due to inaccuracies in the flow regulator. Moreover, after the regulator has been overridden, the arms must be opened or closed fully to realign them. Another problem with flow regulation is that such a control system is not readily compatible with modern adaptive clamping systems, i.e., systems which automatically control the maximum fluid clamping pressure in relation to the sensed weight of the load to be clamped, to avoid overclamping of the load.
Mechanical, rather than flow-regulating, solutions to the foregoing problems of synchronizing the movements of separately-actuated clamp arms have been attempted in the past. These alternative solutions interconnect the separately-actuated clamp arms by means of mechanical linkages which permits only a limited range of movement between the clamp arms. Such mechanical linkages include simple flexible or articulated tether-type links, or mechanical or hydraulic balance-beam links, which prevent more than a predetermined misalignment of the clamp arms. These linkages, however, share the common problem that they do not automatically correct misalignment of the clamp arms to minimize their combined thickness, nor do they always avoid striking a single load engaged by one of the clamp arms when the other clamp arm is not engaging a load.
Other previous linkage mechanisms include a spring-biased detent assembly tending to hold separately-actuated clamp arms in alignment with each other, but allowing large deviations from alignment whenever the spring-biased holding force of the detent is overcome by the fluid power actuators of the clamp arms. Such an arrangement provides neither adequate limitations on the misalignment of the clamp arms, nor sufficient correction of such misalignment. Moreover, when only a single abbreviated-length load is to be handled, clamping pressure on the load-engaging clamp arm cannot be attained until the other clamp arm is fully closed.